Field of the Invention
The present invention relates to a brazing material and a sealing method using the brazing material. In particular, the present invention relates to a brazing material used for hermetically sealing a package for various electronic components. The present invention provides a brazing material which is not remelted, e.g., upon mounting to a board without giving damage to a device inside the package upon sealing and has suitable properties.
Description of the Related Art
Electronic components such as an SAW filter and a crystal oscillator used in various types of electronic equipment such as a cellphone are hermetically sealed in a package made of ceramics or the like in view of protecting an internal device. A brazing material for sealing the package has progressively been made lead-free in view of recent environmental protection. In this view, a Au—Sn brazing material (particularly, a Au-20 wt % Sn brazing material having an eutectic composition) is generally used (Patent Document 1). An advantage of the Au—Sn brazing material is that the Au—Sn brazing material enables an efficient sealing operation upon sealing the package since the Au—Sn brazing material has a comparatively low melting point of about 280° C.
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-150182
Although the Au—Sn brazing material has preferable properties upon the sealing operation of the package, the Au—Sn brazing material also has a problem. The problem is caused when the sealed package is mounted to a board. Since a temperature upon mounting is close to the melting point of the Au—Sn brazing material, the heat remelts the brazing material to cause peeling and leak of the sealed part of the package. Another problem to be concerned about, other than the case where the package is mounted to the board, is that when the board is heated to collect damaged parts in repairing the electronic equipment, the heat may break the sealing of other non-damaged parts.
The remelting of the brazing material is caused by the low melting point of the brazing material. Then, brazing materials having some compositions have been proposed in consideration of the problem. For example, Patent Document 2 proposes the application of a Au—Ge brazing material, particularly a Au-12.5% Ge brazing material. The Au—Ge brazing material has a melting point exceeding 360° C. Patent Document 3 proposes a brazing material made of a ternary alloy of Au, Ge and Sn.
Patent Document 2: Japanese Patent Application Laid-Open No. 7-151943
Patent Document 3: Japanese Patent Application Laid-Open No. 2007-160340
Both the Au—Ge brazing material and the Au—Ge—Sn brazing material have a melting point higher than that of the Au—Sn brazing material. The remelting of the brazing materials having a comparatively high melting point after sealing may be reduced.
However, the Au—Ge brazing material tends to have an excessively high melting point. Considering the melting point, a sealing temperature must be set to 400° C. or more. The sealing performed in the high temperature atmosphere increases the thermal damage of a device inside the package, and may possibly damage the element.
On the other hand, it can be said that the Au—Ge—Sn brazing material minimizes the problem of the damage to the composition upon sealing since the Au—Ge—Sn brazing material has a melting point suppressed to a level lower than that of the Au—Ge brazing material. However, ternary alloys such as the Au—Ge—Sn brazing material may cause a problem of a temperature difference between a liquidus and a solidus. How large or small the temperature difference between the liquidus and the solidus affects workability upon sealing the package. In Patent Document 3, the temperature difference is set to be less than 50° C. However, it is preferable if the temperature difference is small.